With the advent of smart devices, cloud computing, and the Internet of Things (IoT), the bandwidth demands placed upon data centers have increased in leaps and bounds. The reason for this is that mobile and cloud devices are really just terminals, dependent upon centralized data processing and memory capacity in order to deliver the requisite information to the end-user device whose size, cost, and internal computing capability would otherwise be too limited to perform its intended function(s). As bandwidth demands have increased, the demand for optical fiber transmission have likewise increased, not merely in terms of substitution for older copper technologies, but also in terms of quantity, density, and required optical performance.
To meet these demands, a host of different connector interfaces and technologies have been developed, with varying degrees of commercial success. In general, the fiber optic connectors in common use today fall into one of three categories: simplex/duplex connectors, multifiber ferrule connectors, and assembled termini connectors. For many of these connectors, the Telecommunications Industry Association (“TIA”) has defined the mechanical interface requirements, dimensions, and tolerances by means of their Fiber Optic Connector Intermateability Standards (FOCIS).
Simplex/duplex connectors are based upon a single-fiber interface, utilizing a pair of optical ferrules, at least one of which is spring-loaded, along with an alignment sleeve to align these ferrules. A simplex connector contains one of these interfaces, whereas a duplex connector has two identical interfaces arranged side-by-side. Examples of this type include the LC, SC, and MU connectors. These connector types are simple, easy to use, easy to assemble and arrange, inexpensive, and generally offer high optical performance when terminated properly.
Multifiber ferrule connectors, like simplex/duplex connectors, utilize a pair of optical ferrules, at least one of which is spring-loaded, but instead of using an alignment sleeve, the ferrules themselves are gendered, a male ferrule having alignment pins which are accepted by the female ferrule. Further, where simplex/duplex connectors have only one optical fiber terminated within each ferrule, the multifiber ferrule holds an array of fibers within a single aligned interface. By far the most common implementation of this is the MPO connector, which arranges fibers in linear rows of up to twelve (12) fibers per row, and up to six (6) rows of fibers per connector. This creates a fiber contact density which is unrivaled by any other commercial fiber optic connector interface. However, because of the nature of the ferrule termination, termination and polarity options are very limited. Because the fibers are all tied together within a common interface, the precision required for adequate termination is much higher than simplex/duplex connections, and as such optical performance tends to be somewhat poorer, connector cost tends to be higher, or both. Rework and troubleshooting tends to be more difficult, as well, since a problem with one optical channel will by necessity require rework and/or replacement of all lines within the same connector. In particular, multi-row MPO connectors have proven very difficult to reliably manufacture and terminate to acceptable levels of optical performance, especially in singlemode applications which demand more precise fiber alignment.
The third connector type uses an assembled fiber optic terminus, which is a ferrule assembled to a number of related components to mimic the form of an electrical connector contact. Termini themselves are either male (mimicking pin contacts) or female (mimicking socket contacts), and generally allow a fiber optic connection to be substituted for an electrical one, or vice versa. These are common in military style connectors, and military specification MIL-PRF-29504 defines the physical and performance characteristics for the most common types, which are used both in hybrid electrical connectors such as those defined by MIL-DTL-38999 and MIL-DTL-5015, or devoted fiberoptic connectors such as those defined by MIL-DTL-28876. These connectors are robust and reliable, and easy to employ, but since they are based upon electrical contact design and spacing, this utility comes at the expense of the connector's optical channel density and capacity. These connectors are also quite expensive, and labor-intensive at high fiber counts, as each channel must be terminated individually.
At present, those designing connection arrangements for the data center are forced to choose a topology which utilize either simplex/duplex connectors, MPO connectors, or a combination of the two to establish the connections requisite to their respective systems. In general, simplex/duplex connectors are used for patching, while MPO connectors are more commonly employed with trunk and backbone cable assemblies, as the number of fibers within those cable assemblies is often too large for one- and two-fiber connectors to be practicable. This results in topologies which have more connection points than might otherwise be necessary, and polarity arrangements which are inherently inflexible. Since connections are often the primary source of optical insertion loss, the very presence of an MPO connection can endanger loss budgets which are becoming tighter with every passing year. The need for a more flexible multifiber connector solution becomes clear.